Process of separating gasoline from cracked mineral oil



AWM m mm.

A. E. FEW, JR, Er AL,

PROCESS OF' SEPARATING GASOLINE FROM CRACKED MINERAL OIL Filed April 18 1930 WWA/.566.- aM/M.

Patented Apr. 7, 1936 UNITED STATES PATENT OFFICE PROCESS OF SEPARATING GASOLINE FROM CRACKED MINERAL OIL New Jersey Application April 18, 1930, Serial No. 445,280

1 Claim.

The object of the invention is to provide a process of treating a mixture of hydrocarbons produced by cracking so as to recover the lower boiling hydrocarbons. More specifically the object of the invention is to provide a process of treating a cracked crude oil, fuel oil, kerosene, or gas oil (more usually the latter) so as to recover therefrom the gasoline vapors produced by the cracking operation in such condition as will provide a purified, decolorized, anti-knock gasoline having any desired average boiling point and end points. The invention does not `relate to the cracking process per se, which may be effected in vapor phase, mixed phase or the so-called liquid phase, nor does it relate to the process of purifying the separated gasoline vapors, which may `be effected in vapor phase or liquid phase or may be, in exceptional cases, omitted. The process relates to the treatment intermediate between the cracking process and the purification process and has, as one of its important features, the `absorption, from the cracked vapors, of the required amount of heat to effect refluxing by the use, as a main or sole reiiuxing medium, of gasoline of an average boiling point not greatly varying from that of thefgasoline which it is desired to recover as a finished product. The process has, for another important feature, the division of the outflowing gasoline vapors into two streams, one of which is subjected to any desired purification process with or without the removal of a minor proportion of heavy ends, while the other of which is condensed and, without purification `and without necessarily the removal of any heavy ends, is returned to the upper part of the refiuxing tower and utilized as the main or sole refluxing liquid. f

The process may be carried out in apparatus whose structural features are, in large part, known ln the art, and is not, indeed, dependent for its execution on the use of any particular apparatus. An eliicient apparatus for carrying out the process is shown in the accompanying drawing, which is a diagram of a cracking plant, with certain features omitted, including the details of the cracker per se, heat exchangers, etc., forming no part of the present invention.

The gas oil or other hydrocarbon oil to be cracked to gasoline flows 'through any cracking apparatus, such as a coil a within a furnace b. The cracked product thence passes to a locus of reflux condensation, which may be, as shown, a tower d. The cracking may be conducted Vin liquid phase, 'or in vapor phase or in mixed phase, and' in anysuitable cracking apparatus; `the coil a, which is one of the simplest forms of cracking apparatus, being merely a conventional representation of any such apparatus, with the construction and operation of which our invention is not concerned. Whatever may be the cracking process employed, the cracked hydrocarbons enter the tower d either in vapor phase or in mixed liquid and vapor phase. The gasoline constituents, at any rate, will bein vapor phase, :and ordinarily the cracked hydrocarbons will be wholly, or nearly wholly, in vapor phase, 'even if the cracking be performed in so-called liquid phase under high pressure, since the reduction of pressure beyond the pressure control valve c will effect vapcrization of Vmost or all of the constituents.

ln the tower d occurs the reflux .condensation hereinafter described. The desired gasoline constituents escape as vapor at the top-of. the tower through the lines `g and h. The heaviest unvaporized or condensed fraction is precipitated and drawn off, at e, continuously or intermittently, from the bottom of the tower. The intermediate product, which will usually have an average boiling point approximating that of the charging stock, that is, which may be gasoil if the charging stock is gas oil, escapes at -f and may go to storage or rmaybe recycled as charging stock.

The tower d may be of any suitable type known in the art, such as, for example, the bubble tower disclosed in the Pew ,and Thomas Patent No'. 1,723,368, August 6, 1929. Instead of 'flowing the cracked hydrocarbons direct into the tower d, they Ymay first flow into a so-called vaporizer, wherein `a small proportion Vof heavy ends are thrown down, and thence into a tower, as disclosed in the 'Ihomas Patent No. 1,624,692, April 1.2, 1927.

To absorb the required amount of heat to effect reiiuxing there is admitted to the upper part of the tower, through the line p, Va low boiling mixture of hydrocarbons approximately the same as that which it is desired to removeas vapors, and preferably identical therewith except that it contains nolincondensible gases; that is,:if the vapors removed through the line y are those which., except for their content of incondensible gases, it is desired to recover as gasoline, the refluxing liquid admitted to the tower through the line p of gasoline `of substantially the same quality as the outflowing gasoline, the same beingadmitted in such quantity and at suchtemperatureas to absorb precisely the `amountfof yheat that is required to condense .all vapors except those whose separation is desired.

In our process this is effected by splitting the gasoline vapors escaping from the tower into two streams. The streams may escape through independent lines g and h from about the same height, or all the vapors may be withdrawn through the line y and a portion of them diverted through lines h and h.

The gasoline vapors escaping through the line g are condensed and purified in any known manner. Preferably the vapors are passed through a bed of purifying decolorizing material, such as fullers earth, commonly known in the art as a clay tower. Preferably, two of these towers, i, i, are arranged in parallel, only one of them at a time being used. The puried and decolorized gasoline vapors escaping from the clay tower are condensed in one or more condensers y' and thence go to a gas separator lc, wherein the incondensible gases separate and escape through the gas line m. It is preferable, as disclosed in the 'I'homas Patent No. 1,624,692, to effect partial condensation of the gasoline vapors in the clay tower, as set forth in the Thomas patent, this being effected by avoiding the application of heat to the clay tower, with resultant slight drop in temperature of the vapors during their passage therethrough. The condensate escapes through line n and may be returned to the charging stock, or it may be returned to the reiiuxing tower d, or it may be withdrawn from the system.

The gasoline vapors escaping through the line h are condensed in a condenser o and thence go to a gas separator s, wherein the incondensible gases separate and escape through gas line m. The condensed gasoline is pumped through line p and is delivered to the upper part of the tower d as refluxing liquid, as hereinbefore described.

The regulation of the temperature of the condensed gasoline affords no difficulties. It is important to also regulate the proportions of gasoline vapors flowing through lines g and h. This is eiected automatically by maintaining a definite volume of incondensible gas in separator s. When the condensed gasoline in separator s reaches a definite height any suitable float device 1^ throttles, through appropriate connections, a valve t on the gas line m and causes a backing up of gas toward condenser o, thereby reducing the capacity of the condenser and diminishing the flow of gasoline vapors through line h. In practical operation, the proportionate flow of such vapors through lines g and h Will be Subject to little fluctuation.

The pressure maintained in the system is maintained by means of valve v on the gas line m beyond both gas separators.

The process is of particular advantage in the recovery of cracked gasoline from the mixture of hydrocarbons that has been produced by the cracking process, but the process is also applicable to the treatment of the mixture of topped hydrocarbons produced by the partial vaporization, with or Without some incidental cracking, of any mixture of hydrocarbons, particularly crude oil, as, for example, in the topping of crude oil in atmospheric topping stills.

The advantage of my process will be appreciated when it is considered that, in large distillation or cracking units, the use of a gasoline vapor purifying tower oi? the type disclosed in the Thomas Patent No. 1,624,692 hereinbefore mentioned, becomes impracticable due to the great volume of vapors which must iiow through it and due to the practical limit of the size of the tower. We have found that by-passing a comparatively large proportion of the gasoline vapors around the vapor purier back to the tower, with condensation of such vapors in the return flow, avoids imposing an unnecessary burden upon the purifier. We are able, also, by regulating the temperature and rate of return flow of the condensed by-passed gasoline, to insure the outilow from the top of the tower of fractions of no higher boiling point than those which the finished gasoline is intended to contain, thereby avoiding imposing upon the tower the burden of condensing such higher boiling fractions. Finally, by providing two purifiers and using them alternately, we are able to insure the continuous operation of the process, since either purifier that is in operation may be shut down, cleaned and recharged and the gasoline vapors diverted to the other tower, without interrupting the process. The towers i, i, may be operated in multiple. This may be essential if their size is such as to compel simultaneous operation in order to secure commercially practicable eiciency, as explained in our co-pending application Serial No. 448,196, led April 29, 1930.

In order to give all possible information to those skilled in the art to enable them to successfully practice the process without the necessity for experiment, the following concrete illustrations are given.

When the process is used in the production of cracked gasoline, the amount oi' vapor in one stream that is condensed and pumped back to the refluxing tower may be approximately 21/2 times the amount of vapor that goes to the purifier and is condensed as a iinal product. This proportion is susceptible to considerable variation, but in most, if not all, cases, the stream of vapor that is to be condensed and pumped back to the tower is of considerably greater volume, during any given period of time, than the stream of vapor that is to be purified and condensed as a nal product.

In crude oil distillation, there is a similar, but usually greater, excess of volume of one stream of vapors over the other; the ratio of vapors in the stream to be condensed and used as reflux varying from 21/2 to '7 times the volume of vapors of the stream that is puried and condensed as a nal product. In crude oil distillation, the percentages of the two streams will vary within wider limits than in the production of cracked gasoline. As one example, assume that 70% of the crude ls vaporized in a pipe still and that the overhead product in the reiiuxing tower is 5% of the crude,

with a liquid side stream amounting to and the residual oil amounting to 30%. In that case, the vapors to be condensed and reuxed would be about six times the vapors to be puried and condensed as the nal product. Assume, again, that only 50% of the crude is vaporized in a pipe still and that the overhead product is 30%. In that case, the ratio of reflux to iinal product would be about 2% to 1.

While the temperature maintained at the top of the tower is of great importance, it will necessarily vary with the type of product to be obtained and with the pressure. In atmospheric distillation, when gasoline of various types is to be produced, the temperature at the top of the tower will usually vary from 210 to 290 F. and may be somewhat higher. In the production of gasoline by the cracking process, where the tower may be under from 30 to 50 inches of pressure, the temperature will vari7 from 300 to 400 F.

We are aware that it is known to flow vapors,

flowing from the top of a fractionating column, through a partial condenser, wherein a sufficient quantity is condensed to serve as a reflux liquid for the fractionating column. In such a process, however, the part that is condensed is necessarily composed of substantially higher boiling fractions than the part that is not condensed. The reflux liquid is not only composed of higher boiling fractions than those fractions which are not condensed in the fractional condenser, but it is of higher average boiling point than the vapors that escape from the top of the tower. A part of this reflux liquid is revaporized and escapes with other vapors flowing to the fractional condenser. The fractional condenser therefore regulates the constituents of the vapor that is not condensed therein and that, after purification and condensation, is the ultimate 10W boiling product (e. g. gasoline) desired. The fractional condenser is thus as much a unitary part of the fractionating column as any reilux condenser at the top of a column, such, for example, as the reilux condenser of the Thomas patent hereinbefore mentioned. In our process, the gasoline that is pumped back into the tower as a reflux is composed of the same fractions as the gasoline that escapes from the top ofthe tower and is composed of the same fractions as the gasoline that goes to the purier.

Having now fully described our invention, what we claim and desire to protect by Letters Patent ls:

The process of separating hydrocarbons of different boiling points containing a mixture of hydrocarbon vapors including low boiling hydrocarbons which it is desired to separate and of economically purifying the low boiling product desired, which comprises subjecting said hydrocarbons to reflux condensation at the temperature required t-o effect condensation of higher boiling hydrocarbons and separate as vapors approximately the desired lower boiling hydrocarbons, removing from the locus of reux condensation said separated 10W boiling vapors in two vapor streams of like constituents, purifying the vapors of only one stream, separately condensing the puried vapors comprising one stream and the unpuried vapors comprising the other stream, passing the resulting unpuried mixture into an accumulator zone, discharging hydrocarbon gases from the accumulator zone, returning unpurified condensate from the accumulator zone to the locus of reflux condensation an-d thereat utilizing the same as the primary refluxing liquid in the reflux condensation of the mixture of hydrocarbon vapors, and causing the liquid level of the condensate in the accumulator zone to regulate the volume of gases discharged from said zone and thereby regulating the division of vapors into the said two streams.

ARTHUR E. PEW, JR. HENRY THOMAS. 

